In the past, the primary safety control in a scuba diver's propulsion device, be it hand held or worn, has been a momentary type switch. Examples of this can be seen in the devices of Parker U.S. Pat. No. 4,843,998 and Bardoni et al U.S. Pat. No. 3,916,814, as well as the hand held device Takamizawa et al U.S. Pat. No. 4,864,959.
Momentary-type switches, also known as "dead-man" switches are utilized for this application because the switch is normally "open," with its contacts being apart. The scuba diver must "close" the switch by physically and continuously keeping the contacts together. However, for devices that are worn, this conscious effort restricts the use of one of the diver's hands.
A problem with some of the momentary-type switches commonly used is that they rely on some type of water tight seal such as an O-ring or rubber boot to prevent the unwanted intrusion of water from reaching the contacts. Unfortunately, these seals can easily fail.
A solution to this problem was recognized by Takamizawa et al with the use of a reed switch. The reed switch has its contacts hermetically sealed in a glass tube and functions when a magnet pulls its contacts together.
My safety control also uses a hermetically sealed switch but in the form of an opto-electronic device. This device is electrically operated and consists of an infra-red emitter and detector and has no moving parts. Therefore it can be potted into the case along with the rest of the electrical components and thus virtually eliminate the chance of water intrusion.
A movable gate, which does not have to be sealed, serves to function the device by coming between the emitter and detector. Two other opto-electronic devices act in the same manner to function the "power down" and "all stop." The "power up" optoelectronic device, which hereinafter shall be referred to as an ISO (isolation switch, optical), is powered by the same battery which is used in a highly novel safety feature of my control, the ascent limiter.
The novel ascent limiter in accordance with my invention utilizes a standard dive computer to interrupt the electrical power supplied to the propulsion motor should a safe ascent rate be exceeded. In this instance, a Marathon dive computer made by Orca Industries (U.S. Pat. No. 4,192,001) was used. Should the battery in the computer go dead, the ISO cannot start the "power up" function of the conventional electronic motor control. By way of example, a Minn Kota (Mankato, Minn.) motor control was used.
Furthermore, should the dive computer fail altogether, the control has a pitch angle limiter which, through the use of mercury switches, again interrupts the electrical power supplied to the propulsion motor. This occurs when a predetermined horizontal position for the scuba diver has been exceeded.
These safety features are very important because a scuba diver could seriously or fatally injure himself or herself if the propulsion device was operated in a careless manner.